Internet-Draft | YANG-CHARRA for TPMs | July 2024 |
Birkholz, et al. | Expires 30 January 2025 | [Page] |
- Workgroup:
- RATS Working Group
- Internet-Draft:
- draft-ietf-rats-yang-tpm-charra-23
- Published:
- Intended Status:
- Standards Track
- Expires:
A YANG Data Model for Challenge-Response-based Remote Attestation Procedures using TPMs
Abstract
This document defines YANG Remote Procedure Calls (RPCs) and a few configuration nodes required to retrieve attestation evidence about integrity measurements from a device, following the operational context defined in TPM-based Network Device Remote Integrity Verification. Complementary measurement logs are also provided by the YANG RPCs, originating from one or more roots of trust for measurement (RTMs). The module defined requires at least one TPM 1.2 or TPM 2.0 as well as a corresponding TPM Software Stack (TSS), or equivalent hardware implementations that include the protected capabilities as provided by TPMs as well as a corresponding software stack, included in the device components of the composite device the YANG server is running on.¶
Status of This Memo
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
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This Internet-Draft will expire on 30 January 2025.¶
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
1. Introduction
This document is based on the general terminology defined in the [RFC9334] and uses the operational context defined in [I-D.ietf-rats-tpm-based-network-device-attest] as well as the interaction model and information elements defined in [I-D.ietf-rats-reference-interaction-models]. The currently supported hardware security modules (HSMs) are the Trusted Platform Modules (TPMs) [TPM1.2] and [TPM2.0] as specified by the Trusted Computing Group (TCG). One TPM, or multiple TPMs in the case of a Composite Device, are required in order to use the YANG module defined in this document. Each TPM is used as a root of trust for storage (RTS) in order to store system security measurement Evidence. And each TPM is used as a root of trust for reporting (RTR) in order to retrieve attestation Evidence. This is done by using a YANG RPC to request a quote which exposes a rolling hash of the security measurements held internally within the TPM.¶
Specific terms imported from [RFC9334] and used in this document include: Attester, Composite Device, Evidence.¶
Specific terms imported from [TPM2.0-Key] and used in this document include: Endorsement Key (EK), Initial Attestation Key (IAK), Attestation Identity Key (AIK), Local Attestation Key (LAK).¶
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
2. The YANG Module for Basic Remote Attestation Procedures
One or more TPMs MUST be embedded in a Composite Device that provides attestation Evidence via the YANG module defined in this document. The ietf-tpm-remote-attestation YANG module enables a composite device to take on the role of an Attester, in accordance with the Remote Attestation Procedures (RATS) architecture [RFC9334], and the corresponding challenge-response interaction model defined in the [I-D.ietf-rats-reference-interaction-models] document. A fresh nonce with an appropriate amount of entropy [NIST-915121] MUST be supplied by the YANG client in order to enable a proof-of-freshness with respect to the attestation Evidence provided by the Attester running the YANG datastore. Further, this nonce is used to prevent replay attacks. The method for communicating the relationship of each individual TPM to specific measured component within the Composite Device is out of the scope of this document.¶
2.1. YANG Modules
In this section the several YANG modules are defined.¶
2.1.1. 'ietf-tpm-remote-attestation'
This YANG module imports modules from [RFC6991] with prefix 'yang', [RFC8348] with prefix 'hw', [I-D.ietf-netconf-keystore] with prefix 'ks', and 'ietf-tcg-algs.yang' Section 2.1.2.3 with prefix 'taa'. Additionally, references are made to [RFC8032], [RFC8017], [RFC6933], [TPM1.2-Commands], [TPM2.0-Arch], [TPM2.0-Structures], [TPM2.0-Key], [TPM1.2-Structures], [bios-log], [BIOS-Log-Event-Type], as well as Appendix A and Appendix B.¶
2.1.1.1. Features
This module supports the following features:¶
- 'mtpm': Indicates that multiple TPMs on the device can support remote attestation. For example, this feature could be used in cases where multiple line cards are present, each with its own TPM.¶
- 'bios': Indicates that the device supports the retrieval of BIOS/UEFI event logs. [bios-log]¶
- 'ima': Indicates that the device supports the retrieval of event logs from the Linux Integrity Measurement Architecture (IMA, see Appendix A).¶
- 'netequip_boot': Indicates that the device supports the retrieval of netequip boot event logs. See Appendix A and Appendix B.¶
2.1.1.2. Identities
This module supports the following types of attestation event logs: 'bios', 'ima', and 'netequip_boot'.¶
2.1.1.3. Remote Procedure Calls (RPCs)
In the following, RPCs for both TPM 1.2 and TPM 2.0 attestation procedures are defined.¶
2.1.1.3.1. 'tpm12-challenge-response-attestation'
This RPC allows a Verifier to request signed TPM PCRs (TPM Quote operation) from a TPM 1.2 compliant cryptoprocessor. Where the feature 'mtpm' is active, and one or more 'certificate-name' is not provided, all TPM 1.2 compliant cryptoprocessors will respond. A YANG tree diagram of this RPC is as follows:¶
+---x tpm12-challenge-response-attestation {taa:tpm12}? +---w input | +---w tpm12-attestation-challenge | +---w pcr-index* pcr | +---w nonce-value binary | +---w certificate-name* certificate-name-ref | {tpm:mtpm}? +--ro output +--ro tpm12-attestation-response* [] +--ro certificate-name certificate-name-ref +--ro up-time? uint32 +--ro TPM_QUOTE2? binary¶
2.1.1.3.2. 'tpm20-challenge-response-attestation'
This RPC allows a Verifier to request signed TPM PCRs (TPM Quote operation) from a TPM 2.0 compliant cryptoprocessor. Where the feature 'mtpm' is active, and one or more 'certificate-name' is not provided, all TPM 2.0 compliant cryptoprocessors will respond. A YANG tree diagram of this RPC is as follows:¶
+---x tpm20-challenge-response-attestation {taa:tpm20}? +---w input | +---w tpm20-attestation-challenge | +---w nonce-value binary | +---w tpm20-pcr-selection* [] | | +---w tpm20-hash-algo? identityref | | +---w pcr-index* pcr | +---w certificate-name* certificate-name-ref | {tpm:mtpm}? +--ro output +--ro tpm20-attestation-response* [] +--ro certificate-name certificate-name-ref +--ro TPMS_QUOTE_INFO binary +--ro quote-signature? binary +--ro up-time? uint32 +--ro unsigned-pcr-values* [] +--ro tpm20-hash-algo? identityref +--ro pcr-values* [pcr-index] +--ro pcr-index pcr +--ro pcr-value? binary¶
An example of an RPC challenge requesting PCRs 0-7 from a SHA-256 bank could look like the following:¶
<rpc message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"> <tpm20-attestation-challenge xmlns="urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation"> <certificate-name> (identifier of a TPM signature key with which the Attester is supposed to sign the attestation data) </certificate-name> <nonce> 0xe041307208d9f78f5b1bbecd19e2d152ad49de2fc5a7d8dbf769f6b8ffdeab9 </nonce> <tpm20-pcr-selection> <tpm20-hash-algo xmlns="urn:ietf:params:xml:ns:yang:ietf-tcg-algs"> TPM_ALG_SHA256 </tpm20-hash-algo> <pcr-index>0</pcr-index> <pcr-index>1</pcr-index> <pcr-index>2</pcr-index> <pcr-index>3</pcr-index> <pcr-index>4</pcr-index> <pcr-index>5</pcr-index> <pcr-index>6</pcr-index> <pcr-index>7</pcr-index> </tpm20-pcr-selection> </tpm20-attestation-challenge> </rpc>¶
A successful response could be formatted as follows:¶
<rpc-reply message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"> <tpm20-attestation-response xmlns="urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation"> <certificate-name xmlns="urn:ietf:params:xml:ns:yang:ietf-keystore"> (instance of Certificate name in the Keystore) </certificate-name> <attestation-data> (raw attestation data, i.e., the TPM quote; this includes, among other information, a composite digest of requested PCRs, the nonce, and TPM 2.0 clock information.) </attestation-data> <quote-signature> (signature over attestation-data using the TPM key identified by sig-key-id) </quote-signature> </tpm20-attestation-response> </rpc-reply>¶
2.1.1.4. 'log-retrieval'
This RPC allows a Verifier to acquire the Evidence which was extended into specific TPM PCRs. A YANG tree diagram of this RPC is as follows:¶
+---x log-retrieval +---w input | +---w log-type identityref | +---w log-selector* [] | +---w name* string | +---w (index-type)? | | +--:(last-entry) | | | +---w last-entry-value? binary | | +--:(index) | | | +---w last-index-number? uint64 | | +--:(timestamp) | | +---w timestamp? yang:date-and-time | +---w log-entry-quantity? uint16 +--ro output +--ro system-event-logs +--ro node-data* [] +--ro name? string +--ro up-time? uint32 +--ro log-result +--ro (attested_event_log_type) +--:(bios) {bios}? | +--ro bios-event-logs | +--ro bios-event-entry* [event-number] | +--ro event-number uint32 | +--ro event-type? uint32 | +--ro pcr-index? pcr | +--ro digest-list* [] | | +--ro hash-algo? identityref | | +--ro digest* binary | +--ro event-size? uint32 | +--ro event-data* binary +--:(ima) {ima}? | +--ro ima-event-logs | +--ro ima-event-entry* [event-number] | +--ro event-number uint64 | +--ro ima-template? string | +--ro filename-hint? string | +--ro filedata-hash? binary | +--ro filedata-hash-algorithm? string | +--ro template-hash-algorithm? string | +--ro template-hash? binary | +--ro pcr-index? pcr | +--ro signature? binary +--:(netequip_boot) {netequip_boot}? +--ro boot-event-logs +--ro boot-event-entry* [event-number] +--ro event-number uint64 +--ro ima-template? string +--ro filename-hint? string +--ro filedata-hash? binary +--ro filedata-hash-algorithm? string +--ro template-hash-algorithm? string +--ro template-hash? binary +--ro pcr-index? pcr +--ro signature? binary¶
2.1.1.5. Data Nodes
This section provides a high level description of the data nodes containing the configuration and operational objects with the YANG model. For more details, please see the YANG model itself in Figure 1.¶
- Container 'rats-support-structures':
-
This houses the set of information relating to remote attestation for a device. This includes specific device TPM(s), the compute nodes (such as line cards) on which the TPM(s) reside, and the algorithms supported across the platform.¶
- Container 'tpms':
-
Provides configuration and operational details for each supported TPM, including the tpm-firmware-version, PCRs which may be quoted, certificates which are associated with that TPM, and the current operational status. Of note are the certificates which are associated with that TPM. As a certificate is associated with a particular TPM attestation key, knowledge of the certificate allows a specific TPM to be identified.¶
+--rw tpms +--rw tpm* [name] +--rw name string +--ro hardware-based boolean +--ro physical-index? int32 {hw:entity-mib}? +--ro path? string +--ro compute-node compute-node-ref {tpm:mtpm}? +--ro manufacturer? string +--rw firmware-version identityref +--rw tpm12-hash-algo? identityref {taa:tpm12}? +--rw tpm12-pcrs* pcr +--rw tpm20-pcr-bank* [tpm20-hash-algo] {taa:tpm20}? | +--rw tpm20-hash-algo identityref | +--rw pcr-index* tpm:pcr +--ro status enumeration +--rw certificates +--rw certificate* [name] +--rw name string +--rw keystore-ref? leafref {ks:asymmetric-keys}? +--rw type? enumeration¶
container 'attester-supported-algos' - Identifies which TCG hash algorithms are available for use on the Attesting platform. An operator will use this information to limit algorithms available for use by RPCs to just a desired set from the universe of all allowed hash algorithms by the TCG.¶
+--rw attester-supported-algos +--rw tpm12-asymmetric-signing* identityref {taa:tpm12}? +--rw tpm12-hash* identityref {taa:tpm12}? +--rw tpm20-asymmetric-signing* identityref {taa:tpm20}? +--rw tpm20-hash* identityref {taa:tpm20}?¶
container 'compute-nodes' - When there is more than one TPM supported, this container maintains the set of information related to the compute node associated with a specific TPM. This allows each specific TPM to identify to which 'compute-node' it belongs.¶
+--rw compute-nodes {tpm:mtpm}? +--ro compute-node* [node-id] +--ro node-id string +--ro node-physical-index? int32 {hw:entity-mib}? +--ro node-name? string +--ro node-location? string¶
2.1.2. 'ietf-tcg-algs'
This document has encoded the TCG Algorithm definitions of [TCG-Algos], revision 1.32. By including this full table as a separate YANG file within this document, it is possible for other YANG models to leverage the contents of this model. Specific references to [RFC2104], [RFC8017], [ISO-IEC-9797-1], [ISO-IEC-9797-2], [ISO-IEC-10116], [ISO-IEC-10118-3], [ISO-IEC-14888-3], [ISO-IEC-15946-1], [ISO-IEC-18033-3], [IEEE-Std-1363-2000], [IEEE-Std-1363a-2004], [NIST-PUB-FIPS-202], [NIST-SP800-38C], [NIST-SP800-38D], [NIST-SP800-38F], [NIST-SP800-56A], [NIST-SP800-108], [bios-log], as well as Appendix A and Appendix B exist within the YANG Model.¶
2.1.2.1. Features
There are two types of features supported: 'TPM12' and 'TPM20'. Support for either of these features indicates that a cryptoprocessor supporting the corresponding type of TCG TPM API is present on an Attester. Most commonly, only one type of cryptoprocessor will be available on an Attester.¶
2.1.2.2. Identities
There are three types of identities in this model:¶
- Cryptographic functions supported by a TPM algorithm; these include: 'asymmetric', 'symmetric', 'hash', 'signing', 'anonymous_signing', 'encryption_mode', 'method', and 'object_type'. The definitions of each of these are in Table 2 of [TCG-Algos].¶
- API specifications for TPM types: 'tpm12' and 'tpm20'¶
- Specific algorithm types: Each algorithm type defines what cryptographic functions may be supported, and on which type of API specification. It is not required that an implementation of a specific TPM will support all algorithm types. The contents of each specific algorithm mirrors what is in Table 3 of [TCG-Algos].¶
2.1.2.3. YANG Module
<CODE BEGINS> file "ietf-tcg-algs@2022-03-23.yang" module ietf-tcg-algs { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-tcg-algs"; prefix taa; organization "IETF RATS (Remote ATtestation procedureS) Working Group"; contact "WG Web: <https://datatracker.ietf.org/wg/rats/> WG List: <mailto:rats@ietf.org> Author: Eric Voit <mailto:evoit@cisco.com>"; description "This module defines identities for asymmetric algorithms. Copyright (c) 2022 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document are to be interpreted as described in BCP 14 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here."; revision 2022-03-23 { description "Initial version"; reference "RFC XXXX: A YANG Data Model for Challenge-Response-based Remote Attestation Procedures using TPMs"; } /*****************/ /* Features */ /*****************/ feature tpm12 { description "This feature indicates algorithm support for the TPM 1.2 API as per Section 4.8 of TPM1.2-Structures: TPM Main Part 2 TPM Structures https://trustedcomputinggroup.org/wp-content/uploads/TPM- Main-Part-2-TPM-Structures_v1.2_rev116_01032011.pdf"; } feature tpm20 { description "This feature indicates algorithm support for the TPM 2.0 API as per Section 11.4 of Trusted Platform Module Library Part 1: Architecture. See TPM2.0-Arch: https://trustedcomputinggroup.org/wp-content/uploads/ TCG_TPM2_r1p59_Part1_Architecture_pub.pdf"; } /*****************/ /* Identities */ /*****************/ identity asymmetric { description "A TCG recognized asymmetric algorithm with a public and private key."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 2, https://trustedcomputinggroup.org/resource/ tcg-algorithm-registry/TCG-_Algorithm_Registry_r1p32_pub"; } identity symmetric { description "A TCG recognized symmetric algorithm with only a private key."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 2"; } identity hash { description "A TCG recognized hash algorithm that compresses input data to a digest value or indicates a method that uses a hash."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 2"; } identity signing { description "A TCG recognized signing algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 2"; } identity anonymous_signing { description "A TCG recognized anonymous signing algorithm."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 2"; } identity encryption_mode { description "A TCG recognized encryption mode."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 2"; } identity method { description "A TCG recognized method such as a mask generation function."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 2"; } identity object_type { description "A TCG recognized object type."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 2"; } identity cryptoprocessor { description "Base identity identifying a crytoprocessor."; } identity tpm12 { if-feature "tpm12"; base cryptoprocessor; description "Supportable by a TPM1.2."; reference "TPM1.2-Structures: https://trustedcomputinggroup.org/wp-content/uploads/ TPM-Main-Part-2-TPM-Structures_v1.2_rev116_01032011.pdf TPM_ALGORITHM_ID values, Section 4.8"; } identity tpm20 { if-feature "tpm20"; base cryptoprocessor; description "Supportable by a TPM2."; reference "TPM2.0-Structures: https://trustedcomputinggroup.org/wp-content/uploads/ TPM-Rev-2.0-Part-2-Structures-01.38.pdf"; } identity TPM_ALG_RSA { if-feature "tpm12 or tpm20"; base tpm12; base tpm20; base asymmetric; base object_type; description "RSA algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and RFC 8017. ALG_ID: 0x0001"; } identity TPM_ALG_TDES { if-feature "tpm12"; base tpm12; base symmetric; description "Block cipher with various key sizes (Triple Data Encryption Algorithm, commonly called Triple Data Encryption Standard) Note: was banned in TPM1.2 v94"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 18033-3. ALG_ID: 0x0003"; } identity TPM_ALG_SHA1 { if-feature "tpm12 or tpm20"; base hash; base tpm12; base tpm20; description "SHA1 algorithm - Deprecated due to insufficient cryptographic protection. However, it is still useful for hash algorithms where protection is not required."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10118-3. ALG_ID: 0x0004"; } identity TPM_ALG_HMAC { if-feature "tpm12 or tpm20"; base tpm12; base tpm20; base hash; base signing; description "Hash Message Authentication Code (HMAC) algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3, ISO/IEC 9797-2 and RFC2104. ALG_ID: 0x0005"; } identity TPM_ALG_AES { if-feature "tpm12"; base tpm12; base symmetric; description "The AES algorithm with various key sizes"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3, ISO/IEC 18033-3. ALG_ID: 0x0006"; } identity TPM_ALG_MGF1 { if-feature "tpm20"; base tpm20; base hash; base method; description "hash-based mask-generation function"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3, IEEE Std 1363-2000 and IEEE Std 1363a-2004. ALG_ID: 0x0007"; } identity TPM_ALG_KEYEDHASH { if-feature "tpm20"; base tpm20; base hash; base object_type; description "An encryption or signing algorithm using a keyed hash. These may use XOR for encryption or an HMAC for signing and may also refer to a data object that is neither signing nor encrypting."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3, ALG_ID: 0x0008"; } identity TPM_ALG_XOR { if-feature "tpm12 or tpm20"; base tpm12; base tpm20; base hash; base symmetric; description "The XOR encryption algorithm."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3. ALG_ID: 0x000A"; } identity TPM_ALG_SHA256 { if-feature "tpm20"; base tpm20; base hash; description "The SHA 256 algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10118-3. ALG_ID: 0x000B"; } identity TPM_ALG_SHA384 { if-feature "tpm20"; base tpm20; base hash; description "The SHA 384 algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10118-3. ALG_ID: 0x000C"; } identity TPM_ALG_SHA512 { if-feature "tpm20"; base tpm20; base hash; description "The SHA 512 algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10118-3. ALG_ID: 0x000D"; } identity TPM_ALG_NULL { if-feature "tpm20"; base tpm20; description "NULL algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3. ALG_ID: 0x0010"; } identity TPM_ALG_SM3_256 { if-feature "tpm20"; base tpm20; base hash; description "The SM3 hash algorithm."; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10118-3:2018. ALG_ID: 0x0012"; } identity TPM_ALG_SM4 { if-feature "tpm20"; base tpm20; base symmetric; description "SM4 symmetric block cipher"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3. ALG_ID: 0x0013"; } identity TPM_ALG_RSASSA { if-feature "tpm20"; base tpm20; base asymmetric; base signing; description "RFC 8017 Signature algorithm defined in section 8.2 (RSASSAPKCS1-v1_5)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and RFC 8017. ALG_ID: 0x0014"; } identity TPM_ALG_RSAES { if-feature "tpm20"; base tpm20; base asymmetric; base encryption_mode; description "RFC 8017 Signature algorithm defined in section 7.2 (RSAES-PKCS1-v1_5)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and RFC 8017. ALG_ID: 0x0015"; } identity TPM_ALG_RSAPSS { if-feature "tpm20"; base tpm20; base asymmetric; base signing; description "Padding algorithm defined in section 8.1 (RSASSA PSS)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and RFC 8017. ALG_ID: 0x0016"; } identity TPM_ALG_OAEP { if-feature "tpm20"; base tpm20; base asymmetric; base encryption_mode; description "Padding algorithm defined in section 7.1 (RSASSA OAEP)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and RFC 8017. ALG_ID: 0x0017"; } identity TPM_ALG_ECDSA { if-feature "tpm20"; base tpm20; base asymmetric; base signing; description "Signature algorithm using elliptic curve cryptography (ECC)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 14888-3. ALG_ID: 0x0018"; } identity TPM_ALG_ECDH { if-feature "tpm20"; base tpm20; base asymmetric; base method; description "Secret sharing using ECC"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-56A. ALG_ID: 0x0019"; } identity TPM_ALG_ECDAA { if-feature "tpm20"; base tpm20; base asymmetric; base signing; base anonymous_signing; description "Elliptic-curve based anonymous signing scheme"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and TCG TPM 2.0 library specification. ALG_ID: 0x001A"; } identity TPM_ALG_SM2 { if-feature "tpm20"; base tpm20; base asymmetric; base signing; base encryption_mode; base method; description "SM2 - depending on context, either an elliptic-curve based, signature algorithm, an encryption scheme, or a key exchange protocol"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3. ALG_ID: 0x001B"; } identity TPM_ALG_ECSCHNORR { if-feature "tpm20"; base tpm20; base asymmetric; base signing; description "Elliptic-curve based Schnorr signature"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3. ALG_ID: 0x001C"; } identity TPM_ALG_ECMQV { if-feature "tpm20"; base tpm20; base asymmetric; base method; description "Two-phase elliptic-curve key"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-56A. ALG_ID: 0x001D"; } identity TPM_ALG_KDF1_SP800_56A { if-feature "tpm20"; base tpm20; base hash; base method; description "Concatenation key derivation function"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-56A (approved alternative1) section 5.8.1. ALG_ID: 0x0020"; } identity TPM_ALG_KDF2 { if-feature "tpm20"; base tpm20; base hash; base method; description "Key derivation function"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and IEEE 1363a-2004 KDF2 section 13.2. ALG_ID: 0x0021"; } identity TPM_ALG_KDF1_SP800_108 { base TPM_ALG_KDF2; description "A key derivation method"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-108 - Section 5.1 KDF. ALG_ID: 0x0022"; } identity TPM_ALG_ECC { if-feature "tpm20"; base tpm20; base asymmetric; base object_type; description "Prime field ECC"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 15946-1. ALG_ID: 0x0023"; } identity TPM_ALG_SYMCIPHER { if-feature "tpm20"; base tpm20; base symmetric; base object_type; description "Object type for a symmetric block cipher"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and TCG TPM 2.0 library specification. ALG_ID: 0x0025"; } identity TPM_ALG_CAMELLIA { if-feature "tpm20"; base tpm20; base symmetric; description "The Camellia algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 18033-3. ALG_ID: 0x0026"; } identity TPM_ALG_SHA3_256 { if-feature "tpm20"; base tpm20; base hash; description "ISO/IEC 10118-3 - the SHA 256 algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST PUB FIPS 202. ALG_ID: 0x0027"; } identity TPM_ALG_SHA3_384 { if-feature "tpm20"; base tpm20; base hash; description "The SHA 384 algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST PUB FIPS 202. ALG_ID: 0x0028"; } identity TPM_ALG_SHA3_512 { if-feature "tpm20"; base tpm20; base hash; description "The SHA 512 algorithm"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST PUB FIPS 202. ALG_ID: 0x0029"; } identity TPM_ALG_CMAC { if-feature "tpm20"; base tpm20; base symmetric; base signing; description "block Cipher-based Message Authentication Code (CMAC)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 9797-1:2011 Algorithm 5. ALG_ID: 0x003F"; } identity TPM_ALG_CTR { if-feature "tpm20"; base tpm20; base symmetric; base encryption_mode; description "Counter mode"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10116. ALG_ID: 0x0040"; } identity TPM_ALG_OFB { base tpm20; base symmetric; base encryption_mode; description "Output Feedback mode"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10116. ALG_ID: 0x0041"; } identity TPM_ALG_CBC { if-feature "tpm20"; base tpm20; base symmetric; base encryption_mode; description "Cipher Block Chaining mode"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10116. ALG_ID: 0x0042"; } identity TPM_ALG_CFB { if-feature "tpm20"; base tpm20; base symmetric; base encryption_mode; description "Cipher Feedback mode"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10116. ALG_ID: 0x0043"; } identity TPM_ALG_ECB { if-feature "tpm20"; base tpm20; base symmetric; base encryption_mode; description "Electronic Codebook mode"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and ISO/IEC 10116. ALG_ID: 0x0044"; } identity TPM_ALG_CCM { if-feature "tpm20"; base tpm20; base symmetric; base signing; base encryption_mode; description "Counter with Cipher Block Chaining-Message Authentication Code (CCM)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-38C. ALG_ID: 0x0050"; } identity TPM_ALG_GCM { if-feature "tpm20"; base tpm20; base symmetric; base signing; base encryption_mode; description "Galois/Counter Mode (GCM)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-38D. ALG_ID: 0x0051"; } identity TPM_ALG_KW { if-feature "tpm20"; base tpm20; base symmetric; base signing; base encryption_mode; description "AES Key Wrap (KW)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-38F. ALG_ID: 0x0052"; } identity TPM_ALG_KWP { if-feature "tpm20"; base tpm20; base symmetric; base signing; base encryption_mode; description "AES Key Wrap with Padding (KWP)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-38F. ALG_ID: 0x0053"; } identity TPM_ALG_EAX { if-feature "tpm20"; base tpm20; base symmetric; base signing; base encryption_mode; description "Authenticated-Encryption Mode"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and NIST SP800-38F. ALG_ID: 0x0054"; } identity TPM_ALG_EDDSA { if-feature "tpm20"; base tpm20; base asymmetric; base signing; description "Edwards-curve Digital Signature Algorithm (PureEdDSA)"; reference "TCG-Algos:TCG Algorithm Registry Rev1.32 Table 3 and RFC 8032. ALG_ID: 0x0060"; } } <CODE ENDS>¶
Note that not all cryptographic functions are required for use by ietf-tpm-remote-attestation.yang
. However, the full definition of Table 3 of [TCG-Algos] will allow use by additional YANG specifications.¶
3. IANA Considerations
This document registers the following namespace URIs in the [xml-registry] as per [RFC3688]:¶
- URI:
-
urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation¶
- URI:
-
urn:ietf:params:xml:ns:yang:ietf-tcg-algs¶
This document registers the following YANG modules in the registry [yang-parameters] as per Section 14 of [RFC6020]:¶
4. Security Considerations
The YANG module ietf-tpm-remote-attestation.yang specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].¶
There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes as well as their sensitivity/vulnerability:¶
- Container '/rats-support-structures/attester-supported-algos':
-
'tpm12-asymmetric-signing', 'tpm12-hash', 'tpm20-asymmetric-signing', and 'tpm20-hash'. All could be populated with algorithms that are not supported by the underlying physical TPM installed by the equipment vendor. A vendor should restrict the ability to configure unsupported algorithms.¶
- Container: '/rats-support-structures/tpms':
-
'name': Although shown as 'rw', it is system generated. Therefore, it should not be possible for an operator to add or remove a TPM from the configuration.¶
-
'tpm20-pcr-bank': It is possible to configure PCRs for extraction which are not being extended by system software. This could unnecessarily use TPM resources.¶
-
'certificates': It is possible to provision a certificate which does not correspond to an Attestation Identity Key (AIK) within the TPM 1.2, or an Attestation Key (AK) within the TPM 2.0 respectively. In such a case, calls to an RPC requesting this specific certificate could result in either no response or a response for an unexpected TPM.¶
- RPC 'tpm12-challenge-response-attestation':
-
The receiver of the RPC response must verify that the certificate is for an active AIK, i.e., the certificate has been confirmed by a third party as being able to support Attestation on the targeted TPM 1.2.¶
- RPC 'tpm20-challenge-response-attestation':
-
The receiver of the RPC response must verify that the certificate is for an active AK, i.e., the private key confirmation of the quote signature within the RPC response has been confirmed by a third party to belong to an entity legitimately able to perform Attestation on the targeted TPM 2.0.¶
- RPC 'log-retrieval':
-
Requesting a large volume of logs from the Attester could require significant system resources and create a denial of service.¶
Information collected through the RPCs above could reveal that specific versions of software and configurations of endpoints that could identify vulnerabilities on those systems. Therefore, RPCs should be protected by NACM [RFC8341] with a default setting of deny-all to limit the extraction of attestation data by only authorized Verifiers.¶
For the YANG module ietf-tcg-algs.yang, please use care when selecting specific algorithms. The introductory section of [TCG-Algos] highlights that some algorithms should be considered legacy, and recommends implementers and adopters diligently evaluate available information such as governmental, industrial, and academic research before selecting an algorithm for use.¶
5. References
5.1. Normative References
- [bios-log]
- "TCG PC Client Platform Firmware Profile Specification, Section 9.4.5.2", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/PC-ClientSpecific_Platform_Profile_for_TPM_2p0_Systems_v51.pdf>.
- [BIOS-Log-Event-Type]
- "TCG PC Client Platform Firmware Profile Specification", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf>.
- [cel]
- "Canonical Event Log Format, Section 4.3", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TCG_IWG_CEL_v1_r0p41_pub.pdf>.
- [I-D.ietf-netconf-keystore]
- Watsen, K., "A YANG Data Model for a Keystore and Keystore Operations", Work in Progress, Internet-Draft, draft-ietf-netconf-keystore-35, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-keystore-35>.
- [I-D.ietf-rats-tpm-based-network-device-attest]
- Fedorkow, G., Voit, E., and J. Fitzgerald-McKay, "TPM-based Network Device Remote Integrity Verification", Work in Progress, Internet-Draft, draft-ietf-rats-tpm-based-network-device-attest-14, , <https://datatracker.ietf.org/doc/html/draft-ietf-rats-tpm-based-network-device-attest-14>.
- [IEEE-Std-1363-2000]
- "IEEE 1363-2000 - IEEE Standard Specifications for Public-Key Cryptography", n.d., <https://standards.ieee.org/standard/1363-2000.html>.
- [IEEE-Std-1363a-2004]
- "1363a-2004 - IEEE Standard Specifications for Public-Key Cryptography - Amendment 1: Additional Techniques", n.d., <https://ieeexplore.ieee.org/document/1335427>.
- [ISO-IEC-10116]
- "ISO/IEC 10116:2017 - Information technology", n.d., <https://www.iso.org/standard/64575.html>.
- [ISO-IEC-10118-3]
- "Dedicated hash-functions - ISO/IEC 10118-3:2018", n.d., <https://www.iso.org/standard/67116.html>.
- [ISO-IEC-14888-3]
- "ISO/IEC 14888-3:2018 - Digital signatures with appendix", n.d., <https://www.iso.org/standard/76382.html>.
- [ISO-IEC-15946-1]
- "ISO/IEC 15946-1:2016 - Information technology", n.d., <https://www.iso.org/standard/65480.html>.
- [ISO-IEC-18033-3]
- "ISO/IEC 18033-3:2010 - Encryption algorithms", n.d., <https://www.iso.org/standard/54531.html>.
- [ISO-IEC-9797-1]
- "Message Authentication Codes (MACs) - ISO/IEC 9797-1:2011", n.d., <https://www.iso.org/standard/50375.html>.
- [ISO-IEC-9797-2]
- "Message Authentication Codes (MACs) - ISO/IEC 9797-2:2011", n.d., <https://www.iso.org/standard/51618.html>.
- [NIST-PUB-FIPS-202]
- "SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions", n.d., <https://csrc.nist.gov/publications/detail/fips/202/final>.
- [NIST-SP800-108]
- "Recommendation for Key Derivation Using Pseudorandom Functions", n.d., <https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-108.pdf>.
- [NIST-SP800-38C]
- "Recommendation for Block Cipher Modes of Operation: the CCM Mode for Authentication and Confidentiality", n.d., <https://csrc.nist.gov/publications/detail/sp/800-38c/final>.
- [NIST-SP800-38D]
- "Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC", n.d., <https://csrc.nist.gov/publications/detail/sp/800-38d/final>.
- [NIST-SP800-38F]
- "Recommendation for Block Cipher Modes of Operation: Methods for Key Wrapping", n.d., <https://csrc.nist.gov/publications/detail/sp/800-38f/final>.
- [NIST-SP800-56A]
- "Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography", n.d., <https://csrc.nist.gov/publications/detail/sp/800-56a/rev-3/final>.
- [RFC2104]
- Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, , <https://doi.org/10.17487/RFC2104>.
- [RFC2119]
- Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://doi.org/10.17487/RFC2119>.
- [RFC3688]
- Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://doi.org/10.17487/RFC3688>.
- [RFC6020]
- Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, , <https://doi.org/10.17487/RFC6020>.
- [RFC6241]
- Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://doi.org/10.17487/RFC6241>.
- [RFC6242]
- Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, , <https://doi.org/10.17487/RFC6242>.
- [RFC6933]
- Bierman, A., Romascanu, D., Quittek, J., and M. Chandramouli, "Entity MIB (Version 4)", RFC 6933, DOI 10.17487/RFC6933, , <https://doi.org/10.17487/RFC6933>.
- [RFC6991]
- Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, , <https://doi.org/10.17487/RFC6991>.
- [RFC8017]
- Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch, "PKCS #1: RSA Cryptography Specifications Version 2.2", RFC 8017, DOI 10.17487/RFC8017, , <https://doi.org/10.17487/RFC8017>.
- [RFC8032]
- Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital Signature Algorithm (EdDSA)", RFC 8032, DOI 10.17487/RFC8032, , <https://doi.org/10.17487/RFC8032>.
- [RFC8040]
- Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://doi.org/10.17487/RFC8040>.
- [RFC8174]
- Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://doi.org/10.17487/RFC8174>.
- [RFC8341]
- Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://doi.org/10.17487/RFC8341>.
- [RFC8348]
- Bierman, A., Bjorklund, M., Dong, J., and D. Romascanu, "A YANG Data Model for Hardware Management", RFC 8348, DOI 10.17487/RFC8348, , <https://doi.org/10.17487/RFC8348>.
- [RFC8446]
- Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://doi.org/10.17487/RFC8446>.
- [RFC9334]
- Birkholz, H., Thaler, D., Richardson, M., Smith, N., and W. Pan, "Remote ATtestation procedureS (RATS) Architecture", RFC 9334, DOI 10.17487/RFC9334, , <https://doi.org/10.17487/RFC9334>.
- [TCG-Algos]
- "TCG Algorithm Registry", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TCG-_Algorithm_Registry_r1p32_pub.pdf>.
- [TPM1.2]
- TCG, "TPM 1.2 Main Specification", , <https://trustedcomputinggroup.org/resource/tpm-main-specification/>.
- [TPM1.2-Commands]
- "TPM Main Part 3 Commands", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TPM-Main-Part-3-Commands_v1.2_rev116_01032011.pdf>.
- [TPM1.2-Structures]
- "TPM Main Part 2 TPM Structures", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TPM-Main-Part-2-TPM-Structures_v1.2_rev116_01032011.pdf>.
- [TPM2.0]
- TCG, "TPM 2.0 Library Specification", , <https://trustedcomputinggroup.org/resource/tpm-library-specification/>.
- [TPM2.0-Arch]
- "Trusted Platform Module Library - Part 1: Architecture", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TCG_TPM2_r1p59_Part1_Architecture_pub.pdf>.
- [TPM2.0-Key]
- TCG, "TPM 2.0 Keys for Device Identity and Attestation, Rev12", , <https://trustedcomputinggroup.org/wp-content/uploads/TPM-2p0-Keys-for-Device-Identity-and-Attestation_v1_r12_pub10082021.pdf>.
- [TPM2.0-Structures]
- "Trusted Platform Module Library - Part 2: Structures", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TPM-Rev-2.0-Part-2-Structures-01.38.pdf>.
- [UEFI-Secure-Boot]
- "Unified Extensible Firmware Interface (UEFI) Specification Version 2.9 (March 2021), Section 32.1 (Secure Boot)", n.d., <https://uefi.org/sites/default/files/resources/UEFI_Spec_2_9_2021_03_18.pdf>.
5.2. Informative References
- [I-D.ietf-rats-reference-interaction-models]
- Birkholz, H., Eckel, M., Pan, W., and E. Voit, "Reference Interaction Models for Remote Attestation Procedures", Work in Progress, Internet-Draft, draft-ietf-rats-reference-interaction-models-11, , <https://datatracker.ietf.org/doc/html/draft-ietf-rats-reference-interaction-models-11>.
- [IMA-Kernel-Source]
- "Linux Integrity Measurement Architecture (IMA): Kernel Sourcecode", n.d., <https://github.com/torvalds/linux/blob/df0cc57e057f18e44dac8e6c18aba47ab53202f9/security/integrity/ima/>.
- [NIST-915121]
- "True Randomness Can't be Left to Chance: Why entropy is important for information security", n.d., <https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=915121>.
- [xml-registry]
- "IETF XML Registry", n.d., <https://www.iana.org/assignments/xml-registry/xml-registry.xhtml>.
- [yang-parameters]
- "YANG Parameters", n.d., <https://www.iana.org/assignments/yang-parameters/yang-parameters.xhtml>.
Appendix A. Integrity Measurement Architecture (IMA)
IMA extends the principles of Measured Boot [TPM2.0-Arch] and Secure Boot [UEFI-Secure-Boot] to the Linux operating system, applying it to operating system applications and files. IMA has been part of the Linux integrity subsystem of the Linux kernel since 2009 (kernel version 2.6.30). The IMA mechanism represented by the YANG module in this specification is rooted in the kernel version 5.16 [IMA-Kernel-Source]. IMA enables the protection of system integrity by collecting (commonly referred to as measuring) and storing measurements (called Claims in the context of IETF RATS) of files before execution so that these measurements can be used later, at system runtime, in remote attestation procedures. IMA acts in support of the appraisal of Evidence (which includes measurement Claims) by leveraging Reference Values stored in extended file attributes.¶
In support of the appraisal of Evidence, IMA maintains an ordered list (with no duplicates) of measurements in kernel-space, the Stored Measurement Log (SML), for all files that have been measured before execution since the operating system was started.
Although IMA can be used without a TPM, it is typically used in conjunction with a TPM to anchor the integrity of the SML in a hardware-protected secure storage location, i.e., Platform Configuration Registers (PCRs) provided by TPMs.
IMA provides the SML in both binary and ASCII representations in the Linux security file system securityfs (/sys/kernel/security/ima/
).¶
IMA templates define the format of the SML, i.e., which fields are included in a log record. Examples are file path, file hash, user ID, group ID, file signature, and extended file attributes. IMA comes with a set of predefined template formats and also allows a custom format, i.e., a format consisting of template fields supported by IMA. Template usage is typically determined by boot arguments passed to the kernel. Alternatively, the format can also be hard-coded into custom kernels. IMA templates and fields are extensible in the kernel source code. As a result, more template fields can be added in the future.¶
IMA policies define which files are measured using the IMA policy language. Built-in policies can be passed as boot arguments to the kernel. Custom IMA policies can be defined once during runtime or be hard-coded into a custom kernel. If no policy is defined, no measurements are taken and IMA is effectively disabled.¶
A comprehensive description of the content fields in native Linux IMA TLV format can be found in Table 16 of the Canonical Event Log (CEL) specification [cel]. The CEL specification also illustrates the use of templates to enable extended or customized IMA TLV formats in Section 5.1.6.¶
Appendix B. IMA for Network Equipment Boot Logs
Network equipment can generally implement similar IMA-protected functions to generate measurements (Claims) about the boot process of a device and enable corresponding remote attestation. Network Equipment Boot Logs combine the measurement and logging of boot components and operating system components (executables and files) into a single log file in a format identical to the IMA format. Note that the format used for logging measurement of boot components in this scheme differs from the boot logging strategy described elsewhere in this document.¶
During the boot process of the network device, i.e., from BIOS to the end of the operating system and user-space, all files executed can be measured and logged in the order of their execution. When the Verifier initiates a remote attestation process (e.g., challenge-response remote attestation as defined in this document), the network equipment takes on the role of an Attester and can convey to the Verifier Claims that comprise the measurement log as well as the corresponding PCR values (Evidence) of a TPM.¶
The Verifier can appraise the integrity (compliance with the Reference Values) of each executed file by comparing its measured value with the Reference Value. Based on the execution order, the Verifier can compute a PCR Reference Value (by replaying the log) and compare it to the Measurement Log Claims obtained in conjunction with the PCR Evidence to assess their trustworthiness with respect to an intended operational state.¶
Network equipment usually executes multiple components in parallel. This holds not only during the operating system loading phase, but also even during the BIOS boot phase. With this measurement log mechanism, network equipment can take on the role of an Attester, proving to the Verifier the trustworthiness of its boot process. Using the measurement log, Verifiers can precisely identify mismatching log entries to infer potentially tampered components.¶
This mechanism also supports scenarios that modify files on the Attester that are subsequently executed during the boot phase (e.g., updating/patching) by simply updating the appropriate Reference Values in Reference Integrity Manifests that inform Verifiers about how an Attester is composed.¶